In principle, a valve unit for regulating a flow of fluid comprises a valve body which restricts and controls fluid flows through its inside by means of a modulation-sealing system. Thus the fluid flows into an inlet opening of one side of the valve body and flows out through an outlet opening on the opposite side. To operate such a valve body, an actuator is connected upon an interposed flange, producing an intermediate chamber facing the valve between the actuator and the valve body. By means of a lead-through in the flange, the valve is operated by an operating rod of the actuator. The situation of the valve selectively depends on the position of the operating rod, to ensure the valve closes, completely opens or a certain flow is modulated by a rotational or linear movement of the operating rod. In the normal operating condition, no fluid reaches this intermediate chamber facing the valve. However, in the event of a fault, for example, if a sealing diaphragm is damaged (tear in the diaphragm), this intermediate chamber facing the valve fills with the fluid and the operating pressure of the fluid retained in said chamber.
By means of the annular gap between the operating rod and the flange plate, the flow of the fluid is reliably and permanently restricted to a defined permitted maximum for safety reasons. This is achieved by designing the lead-through of the operating rod through the flange with as narrow as possible an interference fit between the operating rod and the flanged plate. The maximum possible flow of the fluid through the annular gap may be adjusted by means of this narrow gap interference fit of the annular gap. The size of the gap thus produced is therefore to be selected very small, so that narrow interference fits between the flange plate and the operating rod are required. Such interference fits are cost-intensive, as they have the condition of a high expense both in the mechanical production of the component parts and in the assembly of the operating rod and the flange.
In DE 60028508T2, a valve unit for controlling a combustible gas is described, which entails increasing the safety against a possible interruption of electrical supply to the electromagnetic drive of an actuator. Therefore, this valve unit is constructed in such a way that two actuators are used for safety reasons. For certain individual cases, such valve systems with two actuators are absolutely necessary. Nevertheless, this raises the problem that at the lead-through points of the operating rods, the narrow interference fit between both of the actuators must be designed twice. This solution is therefore quite expensive and cost-intensive to manufacture. In DE 60028508 there are no lead-throughs. In this case, the actuators themselves are sealed.
Furthermore, in DE 602005001650T2, a housing arrangement of a valve unit is described, which represents a considerable simplification of the other so-called double valve units, where instead of a double valve unit as described previously, a valve body is demanded where only a single valve flap is used. That has the advantage that, as well as the simpler and cheaper construction of this valve unit, considerably less expense is needed in maintenance, which further reduces the cost. In this solution it is also described how the operating rod is lead through a flange and how the seal is provided here by means of a bushing. This proposes that an internal bushing is to be interposed between the flange and the operating rod. However, it is recommended that the bushing is preferably omitted and as there must be a narrow interference fit here, the selection of materials for the cylinder and the operating rod that exhibit a lower degree of friction are recommended, so that no lubricant is required between the flange and the operating rod. In DE 602005001650 the aim is to achieve a light construction of a valve unit and simple maintenance and to realise a lead-through of an operating rod through a flange with the best possible sliding properties—with or without a friction bearing bushing. The arrangement is solely a single bearing position and the length serves solely the bearing or a bearing must exhibit a certain minimum length.
Another technical solution to solve the problems of interruption of electrical supply is described in DE 60221032T2. An additional pre-loaded spring unit is provided here, which as a result of its resilience keeps the closing element inside the valve unit closed. When the valve is opened by means of an arranged direct current motor, in other words, when operating the actuator, a spring unit is further pre-loaded. After the electrical supply is shut down or with an unplanned interruption of electrical supply, the valve flap inside is closed again by the restoring forces of the spring unit. In the same way, a bushing is arranged here between the flange and the operating rod of the actuator where there is the problem of the narrow interference fit between these two component parts here as well. In this case, too, the bushing serves solely to guide the operating rod.